The invention relates generally to the field of treating work surfaces.
It has been known heretofore to clean working surfaces by means of abrasive blasting machines or apparatus of the general character disclosed in the Rose et al. U.S. Pat. No. 3,916,568; the Mead et al. U.S. Pat. No. 2,494,773; and the Bishop et al. U.S. Pat. No. 2,483,176. The blasting machines of these patents are dependent upon the use of a cleaning head in which a nozzle is moved to direct an abrasive-laden high velocity air stream against the working surface. The blasting machines of the character disclosed in these patents have the problem of removing the large amounts of air supplied in the nozzle stream through the air suction connection to the housing, and thus do not achieve the desired automatic balance of incoming and outgoing air within the housing adjacent to the work surface. Moreover, the nozzle stream is of uniform transverse configuration, or the nozzle is moved in a path such that the width of the blasted area will be substantially the same irrespective of the direction of movement of the housing over the work surface.
In order to overcome inherent disadvantages of blasting machines utilizing the high velocity air nozzles, systems have been employed which utilize centrifugal blasting wheels to propel or project the particulate abrasive material. Blasting apparatus of this type is shown in the Goff U.S. Pat. No. 3,788,010 and Fuma et al. U.S. Pat. No. 3,827,188. While these machines have the advantage of eliminating the large quantities of air supplied with the abrasive particles, the apparatus is rather heavy and cumbersome to handle, since the supply of grit or abrasive is carried by the machine and produces additional weight which must be manually shifted by the operator.
The present invention embodies apparatus having the advantages of the nozzle type machines which permit the use of lightweight apparatus by virtue of supplying the abrasive material from a remote source of supply, and at the same time incorporates the features of those machines which utilize centrifugal means for projecting the abrasive against the work surface. As a further feature of the invention, the invention has the further advantage of utilizing a projected stream of particulate abrasive which is transversely shaped to conform generally to an elongated rectangle. Provision is made for rotating the stream of material about its axis so as to be able to vary the width of the abraded area, between a minimum corresponding to the narrow width of the rectangle and a maximum corresponding to the length of the rectangle, when the apparatus is moved in a predetermined direction.